Methane steam reforming is a highly endothermic reaction and results in localised cooling in the reformer unit.
At the temperatures used for steam reforming in a solid oxide fuel cell the kinetics of the steam reforming reaction are extremely rapid. A problem with indirect internal steam reforming in a solid oxide fuel cell is the mismatch between the activity of the steam reforming catalyst and the heat available from the solid oxide fuel cells. As a result a large temperature gradient may be produced along the length of the reformer unit.
This problem may be reduced by using only a small fraction of the available catalyst activity. This may be achieved practically by providing a non-uniform distribution of the catalyst or by providing a diffusion barrier on the surface of the catalyst. Traditionally a catalyst layer is provided on the outer surface of a pellet and a barrier layer is provided on the catalyst layer or a catalyst slurry layer is provided on the interior surface of a hollow support and a barrier layer is provided on the catalyst layer. In both these cases the application of a catalyst or a barrier layer is extremely difficult due to the uneven nature of the surface of the pellet and hollow support and in the case of the hollow support it is extremely difficult to coat the interior surface of the hollow support. Furthermore, the non-uniform distribution of the catalyst layer is also extremely difficult in both these cases.